libext2fs: reject opening a file system where the blocks per group < 8

[thirdparty/e2fsprogs.git] / misc / e2image.8.in

.\" -*- nroff -*-
.\" Copyright 2001 by Theodore Ts'o.  All Rights Reserved.
.\" This file may be copied under the terms of the GNU Public License.
.\"
.TH E2IMAGE 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
.SH NAME
e2image \- Save critical ext2/ext3/ext4 file system metadata to a file

.SH SYNOPSIS
.B e2image
.RB [ \-r | \-Q " [" \-af ]]
[
.B \-b
.I superblock
]
[
.B \-B
.I blocksize
]
[
.B \-cnps
]
[
.B \-o
.I src_offset
]
[
.B \-O
.I dest_offset
]
.I device
.I image-file
.br
.B e2image
.B \-I
.I device
.I image-file

.SH DESCRIPTION
The
.B e2image
program will save critical ext2, ext3, or ext4 file system metadata located on
.I device
to a file specified by
.IR image-file .
The image file may be examined by
.B dumpe2fs
and
.BR  debugfs ,
by using the
.B \-i
option to those programs.  This can assist an expert in recovering
catastrophically corrupted file systems.
.PP
It is a very good idea to create image files for all file systems on a
system and save the partition layout (which can be generated using the
.B fdisk \-l
command) at regular intervals --- at boot time, and/or every week or so.
The image file should be stored on some file system other than
the file system whose data it contains, to ensure that this data is
accessible in the case where the file system has been badly damaged.
.PP
To save disk space,
.B e2image
creates the image file as a sparse file, or in QCOW2 format.  Hence, if
the sparse image file needs to be copied to another location, it should
either be compressed first or copied using the
.B \-\-sparse=always
option to the GNU version of
.BR cp (1).
This does not apply to the QCOW2 image, which is not sparse.
.PP
The size of an ext2 image file depends primarily on the size of the
file systems and how many inodes are in use.  For a typical 10 Gigabyte
file system, with 200,000 inodes in use out of 1.2 million inodes, the image
file will be approximately 35 Megabytes; a 4 Gigabyte file system with 15,000
inodes in use out of 550,000 inodes will result in a 3 Megabyte image file.
Image files tend to be quite compressible; an image file taking up 32 Megabytes
of space on disk will generally compress down to 3 or 4 Megabytes.
.PP
If
.I image-file
is
.BR \- ,
then the output of
.B e2image
will be sent to standard output, so that the output can be piped to
another program, such as
.BR gzip (1).
(Note that this is currently only supported when
creating a raw image file using the
.B \-r
option, since the process of creating a normal image file, or QCOW2
image currently
requires random access to the file, which cannot be done using a
pipe.

.SH OPTIONS
.TP
.B \-a
Include file data in the image file.  Normally
.B e2image
only includes fs metadata, not regular file data.  This option will
produce an image that is suitable to use to clone the entire FS or
for backup purposes.  Note that this option only works with the
raw
.RI ( \-r )
or QCOW2
.RI ( \-Q )
formats.  In conjunction with the
.B \-r
option it is possible to clone all and only the used blocks of one
file system to another device/image file.
.TP
.BI \-b " superblock"
Get image from partition with broken primary superblock by using
the superblock located at file system block number
.IR superblock .
The partition is copied as-is including broken primary superblock.
.TP
.BI \-B " blocksize"
Set the file system blocksize in bytes.  Normally,
.B e2image
will search for the superblock at various different block sizes in an
attempt to find the appropriate blocksize. This search can be fooled in
some cases.  This option forces e2fsck to only try locating the superblock
with a particular blocksize. If the superblock is not found, e2image will
terminate with a fatal error.
.TP
.BI \-c
Compare each block to be copied from the source
.I device
to the corresponding block in the target
.IR image-file .
If both are already the same, the write will be skipped.  This is
useful if the file system is being cloned to a flash-based storage device
(where reads are very fast and where it is desirable to avoid unnecessary
writes to reduce write wear on the device).
.TP
.B \-f
Override the read-only requirement for the source file system when saving
the image file using the
.B \-r
and
.B \-Q
options.  Normally, if the source file system is in use, the resulting image
file is very likely not going to be useful. In some cases where the source
file system is in constant use this may be better than no image at all.
.TP
.B \-I
install the metadata stored in the image file back to the device.
It can be used to restore the file system metadata back to the device
in emergency situations.
.PP
.B WARNING!!!!
The
.B \-I
option should only be used as a desperation measure when other
alternatives have failed.  If the file system has changed since the image
file was created, data
.B will
be lost.  In general, you should make another full image backup of the
file system first, in case you wish to try other recovery strategies afterward.
.TP
.B \-n
Cause all image writes to be skipped, and instead only print the block
numbers that would have been written.
.TP
.BI \-o " src_offset"
Specify offset of the image to be read from the start of the source
.I device
in bytes.  See
.B OFFSETS
for more details.
.TP
.BI \-O " tgt_offset"
Specify offset of the image to be written from the start of the target
.I image-file
in bytes.  See
.B OFFSETS
for more details.
.TP
.B \-p
Show progress of image-file creation.
.TP
.B \-Q
Create a QCOW2-format image file instead of a normal image file, suitable
for use by virtual machine images, and other tools that can use the
.B .qcow
image format. See
.B QCOW2 IMAGE FILES
below for details.
.TP
.B \-r
Create a raw image file instead of a normal image file.  See
.B RAW IMAGE FILES
below for details.
.TP
.B \-s
Scramble directory entries and zero out unused portions of the directory
blocks in the written image file to avoid revealing information about
the contents of the file system.  However, this will prevent analysis of
problems related to hash-tree indexed directories.

.SH RAW IMAGE FILES
The
.B \-r
option will create a raw image file, which differs
from a normal image file in two ways.  First, the file system metadata is
placed in the same relative offset within
.I image-file
as it is in the
.I device
so that
.BR debugfs (8),
.BR dumpe2fs (8),
.BR e2fsck (8),
.BR losetup (8),
etc. and can be run directly on the raw image file.  In order to minimize
the amount of disk space consumed by the raw image file, it is
created as a sparse file.  (Beware of copying or
compressing/decompressing this file with utilities that don't understand
how to create sparse files; the file will become as large as the
file system itself!)  Secondly, the raw image file also includes indirect
blocks and directory blocks, which the standard image file does not have.
.PP
Raw image files are sometimes used when sending file systems to the maintainer
as part of bug reports to e2fsprogs.  When used in this capacity, the
recommended command is as follows (replace
.B hda1
with the appropriate device for your system):
.PP
.br
	\fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
.PP
This will only send the metadata information, without any data blocks.
However, the filenames in the directory blocks can still reveal
information about the contents of the file system that the bug reporter
may wish to keep confidential.  To address this concern, the
.B \-s
option can be specified to scramble the filenames in the image.
.PP
Note that this will work even if you substitute
.B /dev/hda1
for another raw
disk image, or QCOW2 image previously created by
.BR e2image .

.SH QCOW2 IMAGE FILES
The
.B \-Q
option will create a QCOW2 image file instead of a normal, or raw image file.
A QCOW2 image contains all the information the raw image does, however unlike
the raw image it is not sparse. The QCOW2 image minimize the amount of space
used by the image by storing it in special format which packs data closely
together, hence avoiding holes while still minimizing size.
.PP
In order to send file system to the maintainer as a part of bug report to
e2fsprogs, use following commands (replace
.B hda1
with the appropriate device for your system):
.PP
.br
\	\fBe2image \-Q /dev/hda1 hda1.qcow2\fR
.br
\	\fBbzip2 -z hda1.qcow2\fR
.PP
This will only send the metadata information, without any data blocks.
As described for
.B RAW IMAGE FILES
the
.B \-s
option can be specified to scramble the file system names in the image.
.PP
Note that the QCOW2 image created by
.B e2image
is a regular QCOW2 image and can be processed by tools aware of QCOW2 format
such as for example
.BR qemu-img .
.PP
You can convert a .qcow2 image into a raw image with:
.PP
.br
\	\fBe2image \-r hda1.qcow2 hda1.raw\fR
.br
.PP
This can be useful to write a QCOW2 image containing all data to a
sparse image file where it can be loop mounted, or to a disk partition.
Note that this may not work with QCOW2 images not generated by e2image.

.SH OFFSETS
Normally a file system starts at the beginning of a partition, and
.B e2image
is run on the partition.  When working with image files, you don't
have the option of using the partition device, so you can specify
the offset where the file system starts directly with the
.B \-o
option.  Similarly the
.B \-O
option specifies the offset that should be seeked to in the destination
before writing the file system.
.PP
For example, if you have a
.B dd
image of a whole hard drive that contains an ext2 fs in a partition
starting at 1 MiB, you can clone that image to a block device with:
.PP
.br
\	\fBe2image \-aro 1048576 img /dev/sda1\fR
.br
.PP
Or you can clone a file system from a block device into an image file,
leaving room in the first MiB for a partition table with:
.PP
.br
\	\fBe2image -arO 1048576 /dev/sda1 img\fR
.br
.PP
If you specify at least one offset, and only one file, an in-place
move will be performed, allowing you to safely move the file system
from one offset to another.

.SH AUTHOR
.B e2image
was written by Theodore Ts'o (tytso@mit.edu).

.SH AVAILABILITY
.B e2image
is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.

.SH SEE ALSO
.BR dumpe2fs (8),
.BR debugfs (8)
.BR e2fsck (8)